COMMUNICATIONS TROUBLESHOOTING GUIDELINES
Always start troubleshooting by sending from the machine control to DNC. The DNC
software is much more flexible in how it receives data and will not issue an "alarm" like a
machine control. The nature of the data received may help you identify the source of the
Follow these steps if you are having a problem communicating with the machine control.
1. With DNC in Terminal mode send a program from the machine control to the PC.
If the machine "alarms":
The cable may not be connected to the correct port at the machine control. Check the cable
configuration at the machine end, particularly pins 6, 8, and 20.
If the machine acts like it is prepared to send but "sits" continuously in send mode:
A file will not be sent if the CTS line (line 4 or 5 depending on the machine configuration) is
not asserted. The cable should have a jumper between pins 4 & 5, or lines 4 and 5 should
pass through to their compliment lines on the computer end.
If the machine looks like it is trying to send but you receive nothing:
Check the cable. Pins 2 and 3 may need to be swapped to match the send/receive lines on
the machine control with the receive/send lines on the computer. If hardware handshaking
is being used and pins 2 and 3 need to be swapped pins 4 and 5 will also need to be
Check to see that the correct port has been selected. A quick test is to unplug the cable while
trying to send. If an alarm is shown, then the correct port is being addressed.
Check the DNC communications parameters to be sure the correct COM port has been
Try sending to DNC from another machine control or another computer to verify the COM
port is not defective.
If "garbage" prints out on the computer screen while receiving:
The communications parameters are probably mismatched. Check to see that the data types
(ISO, EIA, or ASCII) match. Many machines have a parameter or setting to select between EIA
and ISO. Then check the baud rate.
Other possible sources of "garbage" are long cables, cables with weak connections, cables
running near EMF sources, or ground faults.
2. Once data has been successfully received most cable, machine parameters, and COM
port configuration problems have been eliminated.
Now send from DNC to the machine control. If DNC appears to send the file but the machine
acts like it is not receiving:
Check the file contents. Perform the initial tests with a file which has been received from the
control, not one generated on your CAD/CAM system. Some controls require an end of block
at the beginning of the file or require a program qualifier (like 02213) at the beginning of the
file. Others require a M30, M02, %, or END at the end of the file.
If a partial program is received, blocks of data appear to be dropped, or the machine issues a
data overflow alarm:
Check to make sure handshaking has been properly enabled. If the cable uses only lines 2,3
and 7 select X-ON/X-OFF protocol. (Also referred to as Software Handshaking or DC1/DC3
control codes.) If the machine does not support software handshaking use a cable with pins
4 and 5 connected. This will enable CTS/RTS handshaking.